Waymores

Ok 89 350 TBI... Changed the fuel filer, pump, injectors, pump relay, injector relay, and pressure regulator. I just cant get this thing to start without carb cleaner. And im running out of money quick lol. Im not getting any gas to the injectors on start up, but once i prime it with b12 it fires up and runs great. I guess my question is, what powers the fuel injectors? Or does anyone have any advice?? Anything at all is greatly appreciated

89IROCZ28

iTrader: (14)

I have to assume the fuel delivery system is working, otherwise it wouldn't continue to run. When you first turn the ignition key to the Run position, the fuel pump should run for a couple seconds to pressurize the injectors. There's an oil pressure switch wired into the fuel pump circuit and the fuel pump won't restart until oil pressure is detected by this switch. You may want to check that switch.

Drumer919

His oil pressure switch is fine, we know that cause after the car starts up and builds pressure it continues to run.

Your PCM is bad, the fuel pump output has failed, the oil psi switch is powering it after it starts and builds pressure like you know. It's acting just as it should - as the fail safe power source to the pump in the event of an electrial fault, in your case PCM failure. Of course it only works when the car is already running when the failure occurs and only as a "one last trip so I'm not stranded" sort of thing.

Correct fix - replace PCM

Cheap fix - reground fuel pump relay to a constant ground (pcm switches ground, not 12+ so right now it has no ground) and supply power to the relay from a switched source hot in crank and run (but you might even get by with powering it from a hot during crank only source and then letting it run off the oil pressure switch after that, I wouldnt though.)

1stcamaro85

hey guys. got a 85 305tpi Iroc with similar issue, kinda. bought car with no maf on it and others stuff. ran crappy. just put maf pigtail on yesterday and NO DIfference. idles better but no run. when first started it revs/drives about 70%, after about 1min, nothing but baby 1/8throttle and that's it. hold peddal to floor and just bla,bla,bla is what it does. Checked injectors good, tps is good, iac ok, ecu seems ok,no CEL on, o2 voltage ok, oil pressure ok, so like any tips would be awesome. I think its fuel problem. Will chek fuel pressure and timing friday but any advise would be great.
Please try to PM me cause i can never figure out how to go back to this same thread to see if anyone responds. Computer dummy speakin here fellows. thanks to all and God Bless.

1stcamaro85

yes I bought it and had wires cut and lost so it's a project but body is solid and perfect with no rust and great paint. i know it's difficult to go by when knowing that but most important stuff is there and plugged back in now except EGR stuff. all else is there and supposively opperational. no CEL light and i'know it works good cause it was on the whole time and soon as I plugged MAF back in it went off on that start up.

Damon

During engine start the ECM activates the fuel pump relay to turn on the pump. This is built into it's programming. Once started both the ECM and the oil pressure sending unit can send power to the fuel pump and keep it running (redundant parallel systems). The power supply system through the OPSU does NOT power the FP relay-it's a direct-connect system. If you have above ~6 PSI of oil pressure the OPSU sends voltage directly to the pump.

Agreed with above, sounds like the ECM/relay path for pump power voltage isn't working properly (no fuel pump activation while cranking, but runs when the engine starts). When you turn it to key-on position can you hear the pump run for it's 2 second priming sequence?